1) Field of the Invention
The invention concerns a method and associated apparatus for the direct recovery, following an electrolytic and/or chemical surface treatment, of residual quantities of an aqueous solution adhering to a charge of pourable mass parts in a movable perforated immersion barrel. The immersion barrel is moved to be positioned in a compressed-air chamber, connected to a centrifugal fan, on a carriage of a barrel installation. A current of air flowing transversely through said chamber entrains the solution residue adhering to the charge into a tank located below the chamber.
2) Description of the Prior Art
Such an apparatus for performing the described above method is known from German Patent Specification DE 31 33 629 C2. The immersion barrel which is attached to the carriage is moved out of the treatment solution tank into a compressed-air chamber and when positioned therein, is subjected together with the contained charge of pourable mass parts to an air current, flowing transversely through the barrel and charge. The air current entrains residual solution adhering to the charge and directs it specifically downwards through a longitudinal slot at the base of the compressed-air chamber, returning it into the tank from which it was previously dragged out.
The known compressed-air chamber consists essentially of two movable half-shells, disposed on the carriage and capable of being displaced towards the raised immersion barrel, so as to enclose the immersion barrel on all sides, apart from a narrow, open longitudinal slot on the underside. The compressed-air chamber is connected to a low-pressure fan which delivers the required quantity of air through the two hollow half-shells. Following completion of the blowing operation, the immersion barrel is moved to the next processing station by means of the carriage, the two movable half-shells are removed sideways from the immersion barrel and the latter is lowered into the tank below, containing the next treatment solution.
The displaceable half-shells are hollow and are provided with openings for blowing the current of air therethrough and, if required, also for the passage of rinsing water.
The known method provides for an unpressurized water rinsing of the charge and the barrel both before the blowing operation for removal of the dragged-out residues of treatment solution, and also simultaneously with the blowing operation.
The quantity of water delivered without pressure has an extremely low process efficiency. Water falling in the form of droplets on the perforated immersion barrel rinses only the exterior of the barrel and runs off the latter without significant wetting of the surfaces of the charge of pourable mass parts contained therein.
The described known apparatus furthermore requires a large amount of apparatus. Control systems must be used for the time-dependent closing and opening cycles of the two half-shells, timed to the raising and lowering operation of the immersion barrel. The half-shells are of considerable dimensions, as appropriate to their function, and are accordingly heavy. The mechanism required for carrying and for simultaneously and synchronously moving the two half-shells on the carriage is costly to produce, complex and difficult to service.
comparable problem and solution can be found in the Published Patent Application DE 44 42 160 A1. Similar movable half-shells execute a circular arc movement, approaching from both sides of the immersion barrel when raised on the carriage, so as closely to enclose it. A fan provides a current of air required for entraining the solution residues, transversely through the barrel and the charge. A lower slot remains open between the two half-shells when moved close together, through which the drawn off residue passes into the tank with the treatment fluid located underneath.
The two movable half-shells are each attached to a swivelling support arm connected to a special mechanism, which necessarily has to be disposed above the motor casing of the barrel unit which is moved into the compressed-air chamber.
The aforementioned design solution obviously results in a substantially greater structural height which is disadvantageous for the erection of the barrel installation.
The cost of the production of the proposed apparatus, however, is not reduced in comparison with that according to German Patent DE 31 33 629 C2. The complicated mechanism, which is not easily accessible, is awkward to service; it is also exposed without protection to the corrosive air within the operating room.
Although German Patent Specification DE 38 30 237 C2 proposes a simplified solution to the problem, which obviously reduces the production costs and facilitates servicing, it has disadvantages of a process nature.
A compressed-air hood mounted on the carriage and connected to a compressed-air supply has essentially the spatial form of an upwardly convex half of a rotational cylinder. The barrel, which is moved into and positioned in the hood, is encompassed by the latter over the circumference of its upper half which is not filled with the charge of pourable mass parts. There is thus created a compressed-air chamber whose base is formed by the air-permeable slope surface of the charge, produced by the rotational movement of the barrel.
The quantity of air blown into the barrel cylinder flows transversely through the mass of the charge and through the perforated lower half of the barrel casing, concomitantly drawing off, to a large degree, the residual quantities of the treatment solution adhering to both of the latter, in order to bring them directly into the tank, located underneath, from which they were previously dragged out.
The current of air emerges from the lower half of the barrel cylinder as a free jet. In terms of fluid mechanics, the polygonal circumference of the lower half of the barrel forms the nozzle outlet of the air jet. Irrespective of its emergence speed, an air jet from a rectangular nozzle has a spread angle of approximately 33.degree.. The conical core of the jet is surrounded by a zone in which the emerging air mixes with the surrounding air with a high degree of vorticity. The total quantity of moved air becomes ever greater, the jet speed ever slower and its range shorter.
It is obvious that, with a higher air speed over the surface of the charge parts and of the barrel cylinder, the achievable effect of drawing off the solution residues adhering to both of the latter and of removing them by means of the air current becomes correspondingly greater.
Accordingly, in the apparatus of Patent DE 38 30 237, the cross-sectional area of the nozzle outlet is approximately equal to the sum of the surfaces of three casing sides. Such an outlet nozzle corresponds approximately to half the circumferential circle of the polygonal barrel cylinder. The air current jet spreads radially from it along the barrel, corresponding to a centre angle of about 180.degree..
It has been shown that the spreading air jet containing the entrained solution residues goes beyond the edge of the tank into which the dragged-out residues of the treatment solution are to be returned. Particular difficulties occur in the case of bath solutions with high operating temperatures. Additional constructional measures are required to control and locally limit the resultant development of vapour which spreads out in the manner of a cloud.
In summary, it may be stated that, in many cases, the known apparatus and associated methods according to the prior art are not capable, or are capable only to a limited extent, of fulfilling the stringent requirements of operating practice.